Sigmund Freud publishes “The Interpretation of Dreams”. His central theory is that the unconscious mind drives much of human behaviour even though civilised society stresses the importance of overriding primitive impulses with morality and reason. Yet this constant tension between a person’s repressed drives and his expected social actions often causes psychological distress. Freud suggests that one of the ways this tension is resolved is through the fantasy world of dreams.

He also draws an important distinction between the manifest and latent content of dreams. In his view, the manifest content is the remembered elements of the dream or its apparent narrative. The latent content is the underlying thoughts and wishes the dream represents. Freud argues that this latent content of dreams is based on fantasies related to the emotional experiences of childhood. Through psychoanalysis or “dreamwork,” patients are able to uncover the unconscious wishes or motives that lie behind a particular dream and so gain a greater understanding of themselves.

1929

Hans Berger develops the first electroencephalograph, an instrument for recording the electrical activity in the brain. Commonly known as the EEG or brainwave test, Berger’s invention is now routinely used as a diagnostic test in neurology, psychiatry and brain research.

1936

Walter Freeman and James Watts perform the first lobotomy in America. The procedure involves severing the connections between the prefrontal cortex and the rest of the brain. It is designed to alleviate the symptoms of depression and other psychological disorders and becomes an established procedure. Unfortunately, although some patients show signs of improvement, many also suffer from profound personality changes just as Phineas Gage did after his accident in 1848 (see above).

1950

Karl Spencer Lashley undertakes a series of experiments designed to identify the neural components of memory. He systematically removes different percentages of rats' brains and then tests them in mazes they have run many times before. The result is a gradual, but consistent, decline in their ability to remember the twists and turns of the maze. From these findings, Lashley concludes that there is no singular site for memory in the brain, but rather that it is a holistic process made up of the sum of many neural connections.

1953

Nathaniel Kleitman and Eugene Aserinsky observed rapideye movement (REM) while researching the sleep patterns of children. Until then, scientists had assumed that the brain was inactive during sleep.
Researchers now believe that people experience two kinds of sleep, orthodox and paradoxical, that alternate throughout the night in intervals of about 100 minutes.

Orthodox sleep occupies 80% of the night and does not involve rapid eye movement. Paradoxical sleep (known as REM sleep) makes up the rest of the time and involves bodily movement as well as rapid eye movement. Newborns spend more than 20% of their sleep in the REM phase, which has led researchers to suspect that this part of sleep involves some sort of learning process.